1. Field of the Invention
The present invention generally relates to the fabrication of semiconductor devices, and more particularly, the present invention relates to the formation of a contact having a high aspect ratio in a semiconductor device.
2. Description of the Related Art
Current information media and computer technologies demand higher operating speeds and larger storage capacities from semiconductor devices. Accordingly, developments continue in an effort to improve the integration degree, reliability, and the response speed of the semiconductor devices.
To increase the degree of integration of integrated circuits (ICs) on a semiconductor chip, it has become necessary to form ultra-fine conductive patterns in which the width of conductive lines and the width of conductive contacts penetrating insulating layers are decreased. As a result, the aspect ratios of the contacts penetrating the insulating layers have substantially increased.
Physical vapor deposition (PVD) processes have been widely used to fill contact holes with metal materials so as to form contacts. However, it is generally difficult to completely fill (i.e., without voids) a contact hole of a high aspect ratio using a PVD process.
Accordingly, in an effort to completely fill of a contact hole, a wetting layer can be used to improve adhesive characteristics and re-flow characteristics of the metal fill-material. In this case, the metal material is filled into the contact hole and then reflowed by heat treatment. Also, in this type of process, a barrier layer is deposited to prevent the metal material from diffusing into the insulating layer during the re-flow process.
It is difficult, however, to deposit a barrier layer and a wetting layer at a uniform thickness in contact holes having high aspect ratios. In addition, barrier layers and wetting layers have limited effectiveness in improving adhesion and re-flow characteristics of the metal material and in preventing the metal material from diffusing. Therefore, even in the case where barrier layers and wetting layers are utilized, it is still difficult to completely fill high aspect ratio contact holes without voids.
Examples of methods for forming metal wiring lines including barrier layers and/or wetting layers are disclosed in U.S. Pat. Nos. 6,207,558 (issued to Singhvi et. al.) and 5,094,981 (issued to Chung et. al.).
U.S. Pat. No. 6,207,558 discloses a method of forming a metal wiring line in which a combination barrier-wetting layer is formed to include tantalum, a tantalum nitride layer, tungsten, a tungsten nitride layer or a combination thereof. The method disclosed in U.S. Pat. No. 6,207,558 has an advantage in that the metal wiring line process can be simplified since the barrier-wetting layer functions both as a barrier layer to prevent the metal material from diffusing into a dielectric body and as a wetting layer to improve deposition characteristics of the metal material. It has been found, however, that the barrier properties of the barrier-wetting layer are not always sufficient to prevent the diffusion of metal material into the dielectric.
According to U.S. Pat. No. 5,094,981, a titanium layer is deposited on a structure which includes a contact hole, and then a highly heat-resistant barrier layer, such as tungsten, is deposited on the titanium layer. A metal material is filled into the contact hole after annealing the structure to thereby complete the metal wiring line. When the contact hole makes contact with source/drain regions including impurities on a substrate, the barrier layer including the tungsten prevents the metal material filled into the contact hole from diffusing into the substrate so that the generation of the spiking is prevented. However, this technique suffers a drawback in that titanium and tungsten chemically react with one another, resulting in an increase in contact resistance.
There is a need for an improved method of filling of a contact hole (also called a via hole) having a high aspect ratio without the formation of a void in the filled contact hole.